This invention relates generally to improvements in fluid flow control systems and, more particularly, to a new and improved automatic, self-regulating, highly accurate drop flow control system for parenteral administration (referred to herein as "intravenous administration" or "IV administration") of medical fluids over a wide range of fluid flow rates. More specifically, the invention relates to improvements in IV controllers using electrically actuated IV tube pinchers.
The usual medical procedure for the gradual IV administration of fluids into the human body, such as fluid replacement, liquid nutrients, blood or plasma, makes use of apparatus which is commonly referred to in the medical art as an intravenous solution administration set. The set typically is a disposable plastic product, and comprises a drop chamber adapted to be connected to a fluid source, a length of tubing extending from the chamber to the patient and a valve mechanism, such as a roller clamp on the tubing.
The drip chamber serves the dual function of allowing a nurse or other attendant to observe the rate at which the fluid drips out of the fluid source and also creates a reservoir for the fluid at the lower end of the drip chamber to insure that no air enters the main feeding tube leading to the patient.
While observation of the rate of drop flow via the drip chamber is a simple way of controlling the amount of fluid fed to a patient over a period of time, its ultimate effectiveness requires that a relatively constant vigil be maintained on the drop flow, lest it cease entirely due to exhaustion of the fluid supply or vary unacceptably from the set rate.
By way of example, it has been a common practice in hospitals to have nurse periodically monitor drop flow rate at each intravenous feeding or parenteral infusion station. Such monitoring of drop flow is a tedious and time consuming process, resulting in a substantial reduction of the available time of qualified medical personnel for other important duties. Typically, the nurse monitoring drop flow rate will use a watch to time the number of drops flowing in an interval of one or more minutes, and she will then mentally perform the mathematics necessary to convert the observed data to an appropriate fluid flow rate, e.g., in milliliters per hour or drops per minute. If the calculated flow rate is substantially different than the prescribed rate, the nurse must manually adjust the roller clamp for a new rate, count drops again, and recalculate to measure the new rate.
Obviously, each of the aforedescribed measurements and calculations and flow rate adjustments usually take several minutes time which, when multiplied by the number of stations being monitored and the number of times each station should be monitored per day, can result in a substantial percentage of total personnel time available.
In addition to the aforedescribed difficulties, the IV administration of medical fluids by gravity induced hydrostatic pressure infusion of the liquid from a fluid source suspended above a patient, is susceptible to fluid flow rate variation due to changes in the fluid level in the bottle, changes in temperature, changes in the venous or arterial pressure of the patient, patient movement, and drift in the effective setting of the roller clamp or other valve mechanism pinching the feeding tube. Moreover, there are a number of situations, such as in intensive care, cardiac and pediatric patients, or where rather critical drugs are being administered, where the desired drop flow rate must be capable of precise selection and must not drift beyond certain prescribed limits.
It will be apparent, therefore, that some of the most critical problems confronting hospital personnel faced with a heavy duty schedule and limited time availability are the problems of quickly, easily, reliably and accurately monitoring and regulating drop flow rate in the IV administration of medical fluids.
In recent years, a number of electrical monitoring systems, drop flow controllers and infusion pumps have been developed to accomplish the various tasks of sensing and regulating drop flow rates. However, while such monitoring and drop rate control devices have generally served their purpose, there is a continuing need for improvement in accuracy and precision of adjustment over a wide range of selected flow rates. Difficulties have been experienced in connection with establishing and maintaining such accurate drop flow rates at the extreme ends of the operating range, i.e., at very high flow rates and very low flow rates. Such difficulties are manifested in IV controllers by sticking of the IV tube as it opens and closes at low drop flow rates and failure of the IV tube pincher to completely close off the IV tube at high drop flow rates because the mechanical inertia of the plunger may be too high to respond to each electrical pulse in a very high frequency pulse train.
Hence, those concerned with the development and use of IV fluid administration systems, and particularly those concerned with the design of automatic fluid flow control systems, such as IV controllers, have recognized the need for improved, relatively simple, economical, reliable, stable and accurate devices for fluid flow control which obviate the aforedescribed difficulties. The present invention clearly fulfills this need.